Floor surfacing machines



June 19, 1962 w. E. HOLT 3,039,241

FLOOR SURFACING MACHINES Filed Jan. 18, 1960 INVENTOR.

WILLIAM E. HOLT ATTORN EY United States Patent 3,039,241 Patented June 19 1962 [ice 3,039,241 FLOOR SURFACING MACHINES William E. Holt, 669 20th St., Oakland, Calif. Filed Jan. 18, 1960, Ser. No. 3,065 4 Claims. (Cl. 51-194) The present invention relates in general to the construction and operation of rotary surfacing elements, and more particularly, to cylindrical hollow rotary drums particularly designed and especially useful in floor surfacing machines for supporting and detaohably holding on its circumferential surface a sheet of abrasive material.

In my prior Patent No. 2,437,958 is disclosed such a rotary drum construction in which a drum cushioning element consisting of two substantially semi-cylindrical relatively thin spring steel plates forming a substantially rigid two-part metallic backing sheet shaped to fit around the cylindrical surface of the drum and a continuous layer or sheet of resilient material, such as sponge rubber, shaped to fit around and coextensive with the outer side of the metallic backing sheet and secured thereto substantially throughout its extent, is detachably mounted on the periphery of the drum. Such detachable mounting is highly desirable to permit rapid replacement of the layer of cushioning material when this layer is damaged, as may occur in use. The provisions for this purpose comprise specially designed annular retaining chucks which engage beveled circular edges of the backing plate sections and are held in the edge engaging position by locking means threaded onthe drum shaft and operable by the use of a special wrench. While the described arrangement substantially reduces the time required to replace the cushioning layer as compared to replacement of a cushioning layer permanently attached to-the drum surface, the time required is still substantial.

In accordance with the present invention, the rotary drum and cushioning element backing plate are constructed to further reduce the time required to replace the detachable cushioning element, by a simplified and more effective construction of the provisions for holding the detachable cushioning element on the drum. In particular the circumferential surface of the drum is made of a non-magnetic conductor material, e.g. aluminum, with magnetized metal incorporated at special locations therein for contact with the steel backing sheets of the cushioning element and of suflicient magnetic force alone or in conjunction with the holding effect of the provisions for holding the sandpaper sheet, to hold the detachable cushioning element firmly in position on the drum against the centrifugal and frictional forces present when the drum is rotated in use at its maximum operating speed.

The various features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

Of the drawings:

FIG. 1 is a perspective view of one type of floor surfacing machine for which the invention is particularly adapted;

FIG. 2 is a perspective view of the rotary drum showing the cushioning element about to be secured;

FIG. 3 is a longitudinal section through the drum;

FIG. 4 is an end view of the drum;

FIG. 5 is a fragmentary enlarged transverse section through one end portion of the drum; and

FIG. 6 is an end view of the detachable drum cushioni'n-g element.

In FIG. 1 is illustrated a floor surfacing or sanding machine of a well known type comprising a wheeled housing 10 enclosing a rotary surfacing element 11 mounted on a horizontal axis and driven by an electric motor 12 mounted on the housing. The motor 12 also drives an exhaust fan 13 connected to a dust collecting nozzle (not shown) adjacent the rear side of the surfacing element -11 and arranged to deliver the dust-laden air to a dust bag (not shown). A hinged shield 16 extends across the front of the housing and can be raised from its operating position to permit access to the surfacing element.

The surfacing element 11 comprises a hollow metal drum formed by a cylindrical shell 17 of non-magnetic metal, preferably aluminum, closed at its opposite ends by circular end plates 18 and 19 fitting therein and secured thereto by screws or the like. A circumferential flange 20 on each end plate abuts the corresponding edge of the shell. The drum is rigidly mounted on a drive shaft 21 journalled in bearings mounted in opposite vertical side plates of the housing 10. The projecting end of the shaft 21 is connected by suitable drive means to the electric motor 12. The circumferential shell 17 of the drum has a narrow slot 22 extending across the drum at a small oblique angle to the drum longitudinal axis. A pair of sandpaper clamping rolls 23 and 24 are rotatably mounted in the end plates and arranged parallel and adjacent to the inner end of the slot 22, as shown in FIG. 5. The rolls have projecting squared ends at opposite ends of the drum adapted to be engaged by suitable tools for simultaneously turning the rolls. The portion of each roll Within the drum is flattened along one side 26 and the remaining circum ferential portion knurled. The knurled roll portions cooperate to form a clamping means for the tapered ends of a sheet of abrasive material 28, such as sandpaper or emery cloth, sized to fit around the drum and its ends to be inserted into the narrow slot formed by the flattened roll portions. The rolls are then turned in opposite directions by the operator so as to have the knurled roll portions grip the opposite ends of the abrasive sheet and draw it taut around the drum periphery. A stationary set screw 30 on the drum abuts a pin 31 positioned in a circular groove 29 in each roll to indicate the sheet receiving position of each roll.

The detachable cushioning element consists of a relatively thin backing sheet of magnetic material, preferably two substantially semi-cylindrical thin plates '38 of spring steel, shaped to fi-t around the periphery of the drum with one pair of straight edges substantially in contact and oblique opposite edges extending along and registering with the oblique edges of the drum slot 22 when mounted on the drum.

In assembling the cushioning element, the backing sheet sections are positioned around a master drum and a layer of cushioning material 40, preferably a sheet of sponge rubber, conforming in size and shape to the composite backing sheet, is bent around the sheet and vulcanized thereon substantially throughout its extent. The twopart construction of the backing sheet facilitates the installation and removal of the cushioning element from the drum without removing the drum from the machine.

In accordance with the invention, a series of elongated magnetized inserts 4-2, preferably of Alnico, an alloy of iron, nickel, aluminum and cobalt, are incorporated in the drum shell 17 at longitudinally spaced points along opposite edges of the slot 22. The magnetized inserts may be incorporated in the drum in any suitable manner, such as by casting the magnetic alloy into elongated recesses or openings in the shell 17 or placing permanent magnets in such shell openings and peening the edges to secure the magnets in position. The outer surface of the magnets 42 conforms to the surrounding area of the drum.

The cushioning layer 40 has its outer sheet-contacting surface formed with a series of closely spaced parallel grooves 44 of rectangular cross-section, preferably 4;" square and A" apart. This grooved construction of the cushioning layer aids in the dissipation of heat generated during operation, and also aids in the traction effect on the superposed sheet of abrasive material.

In the original assembly of the rotary surfacing element, the detachable cushioning element is opened to the dotted line position indicated in FIG. 6 and positioned around the shell 17 with its oblique edges aligned with the corresponding edges of the shell slot. The backing sheet closely contacts with the peripheral surface of the shell and the magnets 42 are preferably so spaced and sized to provide sufficient magnetic holding force to hold the cushioning element in that position against displacement under the maximum centrifugal elfect caused by the drum rotation and the maximum friction effect in operation between the floor and abrasive sheet. The sheet of sandpaper or other abrasive material is then wrapped around the drum and cushioning layer and the opposite ends of the sheet bent and inserted through the slot 22 and between the sheet-holding rolls 2,3, 24. When the rolls are turned to tighten the sheet around the drum, an additional cushioning layer holding effect is provided. The rotary surfacing element is then ready for operation. When the cushioning layer is damaged in operation the described operation is reversed and a new cushioning element of similar construction substituted or the damaged element repaired and replaced.

With the described construction, there is a considerable saving in parts costs as compared to the drum construction of my said prior patent, the special holding chucks, holding nut and operating wrench being eliminated. The simplified drum construction substantially reduces the time required for mounting and replacing the cushioning means, with a consequent increase in the production time of the operator.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. A rotary surfacing element for a floor surfacing machine comprising a hollow rotary drum formed by a cylindrical shell of non-magnetic material closed at its ends and having a slot extending lengthwise of the peripheral surface thereof, means within said drum arranged to receive and hold taut the ends of a sheet of abrasive material adapted to fit around said drum, cushioning means for said sheet of abrasive material comprising a circular backing sheet of magnetic metal shaped to fit around said cylindrical shell and a continuous layer of resilient material coextensive with and secured to the outer side of said backing sheet, said backing sheet and layer of cushioning material having spaced edge portions in line with said shell slot, and magnetized metal incorporated in said shell adjacent to and along opposite sides of said slot and adapted to attract and hold said backing sheet with its edge portions aligned with said slot.

2. A rotary surfacing element for a floor surfacing machine comprising a hollow rotary drum formed by a cylindrical shell of non-magnetic material closed at its ends and having a slot extending lengthwise of the peripheral surface thereof and obliquely to the drum axis, means with-in said drum arranged to receive and hold taut the ends of a sheet of abrasive material adapted to fit around said drum, cushioning means for said sheet of abrasive material comprising a circular backing sheet of magnetic metal shaped to fit around said cylindrical shell and a continuous layer of resilient material coextensive with and secured to the outer side of said backing sheet, said backing sheet and layer of cushioning material having spaced oblique edge portions in line with said shell slot, and magnetized meta-l incorporated in said shell adjacent to and along opposite sides of said slot and adapted to attract and hold said backing sheet with its oblique edge portions aligned with said slot.

3. A rotary surfacing element for a floor surfacing machine comprising a hollow rotary drum formed by a cylindrical shell of non-magnetic material closed at its ends and having a slot extending lengthwise of the peripheral surface thereof and obliquely to the drum axis, means within said drum arranged to receive and hold taut the ends of a sheet of abrasive material adapted to fit around said drum, cushioning means for said sheet of abrasive material comprising a circular backing sheet comprising a pair of semi-circular sections of magnetic metal shaped to fit around said cylindrical shell and a continuous layer of resilient material coextensive with and secured to the outer side of said backing sheet, said backing sheet and layer of cushioning material having spaced oblique edge portions in line with said shell slot, and magnetized metal incorporated in said shell adjacent to and at transversely spaced points along opposite sides of said slot and adapted to attract and hold said backing sheet with its oblique edge portions aligned with said slot.

4. A rotary surfacing element for a floor surfacing machine comprising a hollow rotary drum formed by a cylindrical shell of non-magnetic material closed at its ends and having a slot extending lengthwise of the peripheral surface thereof, a sheet of abrasive material adapted to fit around said drum, cushioning means for said sheet of abrasive material comprising a circular backing sheet of magnetic metal shaped to fit around said cylindrical shell and a continuous layer of resilient material coextensive with and secured to the outer side of said backing sheet, said backing sheet and layer of cushioning material having spaced edge portions in line with said shell slot, magnetized metal incorporated in said shell and adapted to attract and hold said backing sheet with its edge portions aligned with said slot, and means within said drum and independent of said magnetized metal arranged to receive and hold taut the ends of said sheet of abrasive material.

References Cited in the file of this patent UNITED STATES PATENTS 2,437,958 Holt Mar. 16, 1948 2,662,353 Bergman et al. Dec. 15, 1953 2,788,743 Schwerin Apr. 16, 1957 

